Group B streptococci have recently emerged as a major etiologic agent in neonatal disease. These organisms produce life-threatening infections in newborns characterized by bacteremia and in many instances by pulmonary involvement or meningitis. This proposal is addressed to a study of the hemolysin (or hemolysins) produced by these streptococci. The hemolysin, which appears to exist in a cell-bound form that can be extracted from the cells, will be purified using appropriate techniques, including chromatography on Sephacyl S-300, hydrophobic chromatography, and polyacrylamide gel electrophoresis (PAGE). The hemolytic substance will be characterized by several procedures including electrophoresis on cellulose acetate PAGE, and thin layer chromatography, as well as by studying the effects of various enzymes and inhibitors on its activity. Hemolysin production will be examind in a large number of group B isolates, and antibody against the soluble and/or cell-bound form of the hemolysin will be prepared. The action of the hemolysin(s) will be investigated using erythrocytes and mammalian cells. Liposomes composed of phospholipids containing different headgroups or various fatty acyl chains will be used to determine the binding site/target of the hemolysin. Finally, the possibility that the hemolysin may contribute to the virulence of group B streptococci will be investigated by studying the cytotoxicity of these organisms for human cells in culture. The effects of inhibitors of the hemolysin and hemolysin-negative mutants will be examined in this model system. In addition, the virulence of hemolysin-negative mutants parental strains will be compared in mice.